Nonvolatile memories (e.g., electrically programmable read-only memories, electrically erasable and programmable read-only memories, Flash memory, ferroelectric memory, magnetoresistive random access memory (“MRAM”), phase change memory and magnetic media such as tapes and disks) retain data stored therein even when electrical power fails or is turned off. The data-retaining ability of such nonvolatile memories makes them attractive for certain memory applications, but also makes them potential targets for unauthorized persons (e.g., spies, hackers, military opponents); these unauthorized persons might wish to read memory contents and/or power up and utilize connected systems that would normally be unavailable to them.
Ferroelectric memory cells may be made with ferroelectric materials such as, for example, strontium bismuth tantalate, denoted “SBT” (optionally doped with niobium), bismuth lanthanum titanate, denoted “BLT” and/or lead zirconium titanate, denoted “PZT” (optionally doped with lanthanum or calcium). SBT, BLT, PZT and other ferroelectric materials have a lattice structure that includes ions that can move among possible ionic sites of the lattice in response to applied electric fields. Ions that move among the possible ionic sites create a charge displacement within the material, which may then act as a switching component in a ferroelectric memory cell.
The ferroelectric memory cell is thus a form of nonvolatile memory; it retains its data contents when power is turned off so long as its memory layer—the ferroelectric layer—remains substantially below the Curie temperature. At or near the Curie temperature, thermal excitation of the lattice overwhelms the forces that hold the ions in specific ionic sites, effectively neutralizing charge displacement that previously existed within the ferroelectric layer.
U.S. Pat. Nos. 5,885,648 and 5,908,658 describe processes for making ferroelectric materials suitable for use in ferroelectric memory and are incorporated herein by reference. U.S. Pat. No. 5,606,146 describes energetic composites and a method of providing chemical energy, and is further incorporated herein by reference. Certain reactive substance pairs disclosed within the '146 patent include CuClO4 and Al, Cu(NO3)2 and Al, CuO and Al, Fe2O3 and Al (also known as thermite), S and Ca, CuO and Mg, TiF4 and Ca, S and Na, S and Mg, and TiF4 and Li.